The invention concerns a mount for mounting tool bits in a recess of a tool bit holder.
A tool bit mount is known from U.S. Pat. No. 3,670,380, wherein the tool bit is held by the conical head of a lockscrew without resting against the bounding walls of a recess of the tool bit holder. The lockscrew abuts against the annular outer edge of a bore of the tool bit. Since the tool itself is not supported by the bounding walls of a recess of the tool bit holder, a longitudinally slit sleeve encompasses the lockscrew and is equipped with a rectangular external circumference. The sleeve serves to position and immobilize the tool bit, i.e., to prevent the rotation of the tool bit. The sleeve extends into a rectangular cross-section recess of the tool bit and into a corresponding, coaxially rectangular recess of the tool bit holder. However, the sleeve does not provide in this known tool bit mounting a radial fixation of the tool. Rather, as explained hereinabove, the fixation of the tool bit in the tool bit holder is attained by the axial tightening of the lockscrew. For the purpose of replacing a tool bit or to rotate a reversible bit, the lockscrew must be screwed out completely from the threading of the tool bit holder.
A tool bit mount is disclosed in U.S. Pat. No. 3,320,654. The bit rests in a recess of the tool holder. A screw extends through a bore in the bit and screws into a hole of the tool holder. A longitudinally slit sleeve is arranged between the screw and the inner wall of the bore. And end of the sleeve remote from the head of the screw rests on a shoulder of the tool bit holder. The head of the screw protruding from the hole of the tool holder has a conical configuration. The inner wall of the longitudinally slit sleeve has a corresponding conical shape. The radial locking action of this known tool bit mount is based on the fact that when the tool bit rests against the bounding walls of the recess of the tool bit holder, the longitudinal axis of the threaded hole of the tool bit holder is eccentric with respect to the conical bore of the tool bit. The radial fixation of the tool bit against the walls of the recess of the tool bit holder is effected by the wedging action of the conical section of the lockscrew and the conical inner area of the longitudinally slit sleeve.
This tool bit mount achieves merely a radial locking effect; the means used for this purpose are expensive, as the lockscrew must have a conical configuration of a special shape and the sleeve itself must have a conical inner part corresponding to the conical area of the lockscrew. The conical configuration of the locking area of the lockscrew acts to weaken the latter in the radial direction. Rotation or removal of the bit cannot be performed until the screw is unscrewed sufficiently to enable the eccentricity between the bit bore and the holder hole to be eliminated.
It is an object of the invention to provide a tool bit mount of the above-described type wherein the bit is securely fixed during cutting, and the installation, removal and/or the rotation of the tool bit (or reversible bit) may be effected without a substantial screwing-out of the screw. Rather, there is to be required by the invention, merely a slight rotation by 90.degree. to 180.degree. of the screw.
A further object of the invention is to obtain a radial locking action of the lockscrew as well as an axial locking effect, which is particularly advantageous, when the tool bit or the reversible bit has a simple or double conical configuration in its central bore.
In addition, it is an object to enable commercially available standard parts or readily produced parts to be employed. This is especially true for the lock screw and the longitudinally slit sleeve.
Any weakening of the above-mentioned parts by special configurations is to be avoided by the present invention. Furthermore, while satisfying the above-cited conditions, an accurately oriented radial stress is to be achieved against the walls of the recess receiving the tool bit. In the bit according to U.S. Pat. No. 3,320,654, which defines a generic type of the mount according to the invention, the rotation of the sleeve around the axis of the lockscrew during tightening cannot be avoided, so that there is a danger that the locking action in the area of the longitudinal slit of the sleeve is effected in a non-uniform manner against the walls of the recess of the toll holder, thereby bending the slit outwardly. Such non-uniform and unsymmetrical radial stresses are to be avoided in keeping with the object of the invention. Furthermore, an accurate linear contact is to be established between the sleeve and the inner wall of the bore in the tool bit of the present invention.